Indicating fuse plug



Oct. 10, 1933. M. ALDEN 1,930,332

INDICA'IING FUSE PLUG Filed Jan. 2, 1932 MLTON A DEN, FW

Patented Oct. 10, 1933 UNITED STATES PATENT OFFICE My invention relatesto protective devices for electric circuits commonly termed fuse plugs.

The main object of my invention is to provide a simple, inexpensive buteffective construction which will indicate unmistakably when it hasblown.

Another object is to provide a construction of this character which issafe and reliable.

I particularly sought to provide indicating means which can be tested byfeeling even when the plug can not be seen.

In its preferred form the invention includes an insulating body formedof two parts connected by a screw shell and containing a fusible link orstrip. An indicating plunger is connected to this fuse strip andnormally held entirely within the plug under pressure of a spring. Whenthe fuse blows the plunger is released and one end of it propelledoutside the plug where it can be seen and felt.

Fig. 1 is a front view of a plug embodying my invention.

Fig. 2 is a longitudinal sectional view showing the parts in the normalposition for use.

Fig. 3 is a cross sectional view on the plane of the line 3-3 of Fig. 2but omitting the spring.

Fig. 4 is a longitudinal sectional view similar to Fig. 2 but showingthe parts in the position which they would occupy when the fuse blows.

Fig. 5 is a detail view showing one method of securing the screw shellin place and venting the chamber.

Fig. 6 is a perspective view showing the fuse strip and indicatingdevice.

The main body consists of the front portion 7 and the rear portion 8.These are formed of suitable insulating material. The front portion, forinstance, may be formed of a molded phenolic condensation product andthe rear portion may 40 be formed of glass. A screw shell 9 connectsthese two parts of the body and this may be formed of metal such asbrass. Preferably this shell has a flange 10 imbedded in the part 8. Theouter end of the shell may be orimped or bent inwardly at 11 into anumber of recesses 12 in the wall 13 of the part 7. The front part 7 andthe sleeve 13 are preferably molded'in one piece in such a way that theycan be made by a two part die.

The recess 12 has an entrance 14 at the front which communicates withthe interior of the sleeve 13 so as to provide a passage for the escapeof gases due to combustion of the fuse. This passage 14 may be made ofany suitable size and the crimped portion 11 of the'shell 9 may berelied upon to close this passage to any desired extent so that thepassage may serve as a relief vent and yet prevent the passage of anysubstantial flame. The center contact disc 15 may have a central tubularportion 16 riveted in the glass disc 8.

. The fuse strip 17 has the end 18 soldered or otherwise suitablyconnected to the shell 9 and the other end 19 soldered to the centercontact disc 15 by a drop' of solder 20. An intermediate portion 21 ofthe fuse strip may be reduced in size to serve as the point of maximumresistance and consequently the point at which the fuse will blow.

The indicating plunger 22 is mounted in position to slide throughopening 23 in the front of the body of the plug, which passage may serveas the means for permitting the escape of pressure from the interior ofthe plug if desired. An arm 24 has a slot 25 to receive the inner end 26of the indicating plunger. This arm 24 also has a notched portion 27adapted to receive the reduced 76 portion 21 of the fuse strip whenturned edgewise. When the strip is then turned to the position shown inFig. 3 it is locked in this notched portion of the arm.

A spring 28 is mounted on the inner end 26 80 of the indicating plungerand presses against one end of the arm 24 was to bias the plunger towardthe front of the plug. The fuse strip 17, however, normally resists thispressure of the spring and consequently the tip of the plunger 22 isnormally flush with the outer sur-- face of the plug indicatingthat theplug is in its normal operative condition.

When the fuse blows the plunger is released and the spring shoots theplunger outwardly where it protrudes as shown in Fig. 4, thus indicatingthat the fuse has been blown.

I prefer to provide guard flanges 29 on opposite sides of the plunger toserve as a protection to the springand also as bailies to prevent thedirect passage of flame from the interior of the chamber through thepassage 23. These flanges also provide means for centering orpositioning the plunger and the spring in the assembly of the parts.

In assembling the plug the arm 24 is slipped onto the tail end 26 of theplunger 22. The contracted portion 21 of the fuse strip is then slippedsideways into the notch 27 and turned 90 degrees. The plunger and thefuse strip are then inserted into the front portion of the body of theplug, leaving the end 18 extending outwardly through the slot 30 at oneside. The spring is then placed on the inner end of .the plunger and thescrew shell and disc 28, which have been previously assembled, areslipped on until the outer end of the sleeve 9 abuts against the flange31.

The plunger 22 is pressed inwardly until its outer end is flush with thefront of the plug, whereupon the end 19 of the fuse strip is soldered inplace so as to hold the indicating plunger in the retracted position.The outer edge of the screw shell 9 is then crimped into a connectionwith one or more of the recesses 12 and the outer end 18 of the fusestrip may be soldered in place if desired.

The flange 31 serves as a hand grip and may be knurled or of anysuitable shape or design.

The outer surface of the plug is preferably recessed as at 32 to providea kind of finger-guide convenient for locating the passage 23 when thefuse is in working condition or locating the indicator when the fuse hasblown.

The end 19 of the fuse link may be flat and the center contact disc 15may be provided with a slot of appropriate shape and size to accommoateit.

The tubular sleeve 13 may be provided with a threaded portion to receivethe threaded sleeve 9 as is frequently done in fuse plug construction.

This fuse plug not only provides a positive indication of its conditionbut the spring tension on the fuse strip aids in rupturing the arc sinceit pulls the fuse apart as soon as it is softened by heat. The arm alsoprovides an insulating barrier between the parts of the ruptured fuselink.

I claim:

- 1. A fuse plug comprising a tubular insulating body part havinginterior flanges forming bai'lies substantially parallel to the axis ofthe plug, a plunger mounted between the said baflies having one endadapted to protrude in an opening in the front of the plug and an armextending from between the bai'iies, a fuse strip connected to said armand normally holding said plunger in position and a spring for actuatingthe plunger when the fuse blows.

v 2. A fuse plug comprising an insulating body part having a tubularsleeve together with in- 1,aso,es2

terior flanges forming baiiles, a'plunger mounted between the saidbafiies and having one end adapted to protrude in an opening in theplug, a fuse strip normally holding said plunger in position and aspring holding said fuse strip under tension for actuating the plungerwhen the fuse blows.

3. A fuse plug comprising an insulating body part having a hand gripportion, together with flanges forming baflies substantially parallel tothe axis of the plug, a plunger mounted between the said baffles havingone end adapted to pro trude through the front of the plug and an armextending from between the bailies, a fuse strip connected to said armand normally holding said plunger in position and a spring engaging saidarm between said baflies for actuating the plunger when the fuse blows.

. 4. A fuse plug comprising an insulating body part having a tubularsleeve and a hand grip portion, together with interior flanges formingbailles substantially parallel to the axis of the sleeve, a plungermounted between the said bafiies and having one end adapted to protrudethrough the front of the plug, a fuse strip normally holding saidplunger in position and a spring engaging said plunger between saidbaffles for actuating the plunger when the fuse blows.

5. In a construction of the character described, a plug having a bodyportion, a plunger adapted to protrude from the front thereof, aninsulating arm secured to said plunger and hav-- ing an open notchedend, and a flat fuse strip having a reduced portioninterlocked with thenotched end of said arm, said arm being interposed between the parts ofthe fuse when it blows.

6. A fuse plug having a body portion, a plunger adapted to protrudetherefrom and having an open notched portion of insulating material, aflat fuse strip having a reduced portion interlocked with the notchedend of said arm and a spring holding the inner end of the strip undertension and tending to protrude the end of the plunger when the fuseblows.

MILTON ALDEN.

